The use of ultraviolet (UV) disinfection for drinking water treatment
is expected to increase as a result of the Long-Term 2 Enhanced Surface
Water Treatment Rule (LT2ESWTR) (US EPA, 2006a) and Stage 2 Disinfection/Disinfection
Byproducts Rule (US EPA, 2006b).

In order for utilities to receive inactivation credits for UV under
the LT2ESWTR, systems must first be validated under the specific
design configuration and operating conditions planned for full-scale
treatment. Such validation uses costly biodosimetry methods
and must be re-done if a utility desires to change their configuration
or operation of the UV system.

CFD is a modeling tool that has been shown to successfully determine
relative differences in UV reactor performance. A CFD model
provides detailed information on flow-field characteristics that
can aid in identifying hydraulic-based reasons for variations in
reactor performance. CFD thus holds promise as an alternative
for expensive biodosimetry validation methods and a potential substitute
for revalidation.

CFD simulations of UV radiation field with three lamps on (left) and
particle tracks colored by dose with one lamp on (right) in a UV
reactor for water disinfection.

In many cases, utilities will be retrofitting UV systems into existing
treatment processes, so they will be limited in their available inlet/outlet
configurations and may not be able to achieve optimal configurations. Thus,
utilities need a tool to assess hydraulic impacts on UV disinfection performance
and evaluate alternative configurations early in the design process. Moreover,
a better understanding of the effects of inlet/outlet hydraulic configurations
on UV disinfection performance will result in more pragmatic design recommendations,
with potential to significantly reduce capital costs in future UV installations.

CFD holds promise as an alternative for expensive biodosimetry validation
methods and a potential substitute for revalidation. However, CFD has
not yet achieved regulatory acceptance, and the numerous options
and approaches for CFD modeling make it nearly impossible to prescribe
a universally applicable model and approach for any given site. Therefore,
the goal of this project is not to develop a universal CFD model
that will be broadly applicable to UV disinfection systems. Rather,
the objective of this project is to evaluate the effectiveness of
CFD as a tool to assess the impact of design and operational changes
on desired performance objectives such as UV dose distribution and
the resulting reduction equivalent dose.